In a conventional circuit arrangement of this type, each of the two paired transistors is joined by its emitter to a respective current generator connected in series therewith across the d-c source. The two wires of the transmission line are respectively tied to these emitters to form a loop across a remote load through which line current passes via the momentarily more conductive driving transistor and the current generator in series with the momentarily less conductive transistor which is prevented by that generator from being completely cut off. The total power consumption in the output stage is the sum of the wattages dissipated by the biasing currents of the two generators and the line current traversing the more conductive transistor under the control of the binary signal fed to the input stage. Additional power, but of considerably lesser magnitude, is also consumed in that input stage which generally includes another current generator connected in parallel to the emitters of a pair of control transistors, usually of the same structure and conductivity type as the driving transistors of the output stage, whose collectors are respectively tied to the bases of the driving transistors and are connected via respective resistors to the same source terminal as the collectors of the driving transistors.
This large power consumption not only dissipates considerable electrical energy but also requires the use of transistors capable of sustaining same, which may affect the reliability of their response to the incoming signal. The power-consumption and dimensioning problems are particularly critical when the driving transistors of the output stage are to form part of an integrated circuit included, for example, in a signal transceiver.